JP2005118969A - Method for stably polishing silicon wafer having high flatness - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably improve processing accuracy of a workpiece in a polishing device for simultaneously polising both surfaces of the workpiece such as a silicon wafer. <P>SOLUTION: A noncontact displacement gauge 26 is installed in three places of the inner periphery, the center and the outer periphery of a width of a polishing plate; to read a surface shape of pads from a shape displacement quantity of a processing surface of the upper and lower polishing pads in polishing processing, for controlling a flow rate and the temperature of cooling water for holding the temperature of the upper and lower polishing plates 21 and 20, a flow rate and the temperature of an abrasive assistively provided for the polishing processing so that upper and lower polishing pad surfaces changing in a recessed or projecting shape become a plane. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to the planar shape of a polishing pad surface of a polishing apparatus for a semiconductor substrate such as a silicon wafer, and in particular, the surface of the pad being polished is always controlled to be highly flat to improve the stability of processing accuracy. Is.

  Since the processing of a workpiece by a surface polishing machine is a processing technology that transfers the accuracy of the surface plate to the workpiece, it is necessary to always maintain the surface plate on a highly accurate plane. However, polishing of silicon wafers, etc. is performed by sandwiching a silicon wafer held by a carrier between upper and lower surface plates in which a pad, which is a polishing cloth, is bonded to the processing surface of the upper and lower polishing plates, and colloidal into the processing liquid of PH 9-12. This is performed by chemical and mechanical combined polishing called the mechanochemical method while supplying an abrasive made of turbid silica to the processed surface. The details of this processing are as follows. While etching the processing surface of the silicon wafer with a processing solution of PH 9-12, colloidal silicon oxide is solid-phased on the processing surface, and the silicon oxide solid-phased on the processing surface is processed on the upper and lower polishing plates. The processed surface of the silicon wafer is polished by repeating mechanical peeling with a pad which is a non-woven fabric affixed to the substrate. This processing method promotes chemical processing by the temperature caused by friction between the pad and the silicon wafer, but if the temperature is too high, the processed surface becomes an orange skin called orange peel, and the pad is attached. The attached upper and lower polishing plates are subject to repeated polishing and wear of the pad, and the friction coefficient changes every moment. A flat silicon wafer cannot be obtained.

  In the conventional method, the planar shape of the upper and lower polishing plate surfaces before processing was measured in a stationary state. However, when the polishing operation is activated, the planar accuracy of the upper and lower polishing pad surfaces is sometimes increased due to heat generated from the bearings. It changes every moment.

  In addition, in order to correct the flatness deterioration of the upper and lower polishing pad surfaces due to the temperature change of the upper and lower polishing plates during this processing, the temperature of the cooling water supplied and discharged into the cooling jacket of the upper and lower polishing plates is measured or polished. Measure the temperature of the upper and lower polishing pad surfaces, and control the flow rate of cooling water or the flow rate or temperature of the polishing agent provided during polishing so that the processing surface temperature of the upper and lower polishing plates becomes a preset value. It was. Specifically, a polishing apparatus described in Japanese Utility Model Publication No. 5-21320 is known, and FIG. 2 shows a part of a temperature detecting unit and a cooling unit in the configuration. In the figure, 11 is a polishing plate, 19 is a pad, 15 and 16 are pipes for circulating a coolant, 12 is a coolant circulation tank, 14 is a coolant circulation pump, and 13 is a coolant in the circulation tank. It is a cooling coil for cooling. Then, the processing surface temperature of the pad 19 is detected by the temperature sensor 17, and the rotational speed of the electric motor in the coolant circulation pump 14 is controlled via the control circuit 18 in accordance with this temperature to control only the flow rate of the coolant. Thus, the cooling liquid is continuously circulated through the polishing platen 11 to keep the temperature constant, thereby maintaining the flat surface of the pad 16 of the polishing plate.

Although not shown, a temperature sensor is embedded in the rotating polishing platen, a temperature signal transmitting antenna is attached to the outer periphery of the polishing platen, and the receiving control circuit is separately installed and operated by a receiving control circuit for cooling. There is also a method of keeping the temperature of the processing surface of the polishing platen constant by controlling the rotation speed of the liquid circulation pump.
No. 5-21320

  However, the method of controlling the temperature of the upper and lower polishing plates is that the pad attached to the polishing plate is made of a material in which a resin is infiltrated into a nonwoven fabric, so the thermal conductivity is poor, and the surface temperature of the pad during processing The surface temperature of the surface of the polishing plate where the pad is attached has a slight temperature difference of several degrees, and the processing surface of the pad is slightly displaced in a concave or convex shape due to this temperature difference, so a high-precision flat surface can be expected. Absent.

  For this reason, in the polishing process site, a polishing method may be employed in which the surface temperature of the pad is maintained at a constant temperature that seems to be an appropriate temperature by adjusting the flow rate of the abrasive. However, this method of adjusting the flow rate of the abrasive to keep the pad temperature constant cannot maintain a stable accuracy due to fluctuations in the mechanochemical action of the abrasive. Further, in order to maintain stable accuracy after processing without adjusting the flow rate of the abrasive as described above, processing conditions such as load, polishing plate rotation speed, and processing interval must be found.

  Therefore, the present invention pays attention to the difference between the material of the polishing plate being processed and the pad affixed to the polishing plate and the thermal displacement due to the change over time, and the surface of the pad that affects the accuracy after processing always keeps the plane. Thus, stable accuracy is maintained by a polishing method of complex correction in which the temperature and flow rate of the cooling water fed to the polishing plate and the flow rate and temperature of the abrasive are controlled in an auxiliary manner.

  The amount of displacement of the processed surface of the upper and lower polishing pads during polishing is changed to concave or convex by reading the surface shape of the pad by attaching non-contact displacement meters to the inner, middle and outer circumferences of the width of the polishing plate. The flow rate and temperature of the cooling water that keeps the temperature of the upper and lower polishing plates, and the flow rate and temperature of the abrasive that is supplied to the polishing process in a supplementary manner are controlled so that the upper and lower polishing pad surfaces to be flattened.

  As described above, the surface shape of the upper and lower polishing pad surfaces that are displaced concavely or convexly due to the friction between the pad and silicon wafer generated during polishing and the change in the amount of heat generated around the polishing apparatus is constantly measured with a non-contact displacement meter. Since the flow rate and temperature of the cooling water fed to the polishing plate are controlled immediately in order to detect and maintain the temperature to hold the upper and lower polishing pad surfaces flat, the processing surface of the upper and lower polishing pads is always maintained flat, Highly flat silicon wafers can be polished stably.

Hereinafter, a planar polishing apparatus according to the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a main part of an embodiment of the present invention, in which 25 is a lower polishing pad and is attached to a 20 lower polishing plate. Reference numeral 24 denotes an upper polishing pad, which is attached to the 21 upper polishing plate. The 27 carrier, which is a jig held by the 20 lower polishing plate and the 21 upper polishing plate, holds the silicon wafer 28 as a work, and the 27 carrier rotates while meshing with the 23 central gear and the 22 internal gear. Perform a revolving planetary motion. The clearance between the 24 upper polishing pad and the 25 lower polishing pad due to the heat generated by the polishing process is set to 26. The clearance between the pads at each position is determined by 26 non-contact displacement meters attached to the inner periphery, middle side, and outer periphery of the upper polishing plate width. Measure and send data to the control circuit. The control circuit computes and issues a command to the 14 cooling liquid circulation pump and the 32 cooling temperature control device that controls the temperature of the cooling liquid. Thus, the surface shape that immediately detects the interval between the 24 upper polishing pad and the 25 lower polishing pad generated by the polishing process and the ambient temperature change, and the measured values of the inner, inner and outer non-contact displacement meters are always equal. Hold.

  FIG. 3 is a cross-sectional view of a main part in which a 26 non-contact displacement meter is incorporated in the middle position of the 21 upper polishing plate. Reference numeral 25 denotes a lower polishing pad, which is attached to a lower 20 polishing plate. Reference numeral 24 denotes an upper polishing pad, which is attached to the 21 upper polishing plate. The gap between the pads is measured with a 26 non-contact displacement meter, and the data is transferred to the 18 control circuit.

It is sectional drawing of the principal part which shows one Example by this invention. The cross-sectional perspective view which shows the temperature control method of the conventional grinding | polishing plate. Sectional drawing of the non-contact displacement meter incorporated in the middle position of the polishing plate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Polishing surface plate 12 Coolant circulation tank 13 Cooling coil 14 Coolant circulation pump 15 Coolant feed circulation pipe 16 Coolant return circulation pipe 17 Temperature sensor 18 Control circuit 19 Pad 20 Lower polishing plate 21 Upper polishing plate 22 Internal gear 23 Center Gear 24 Upper polishing pad 25 Lower polishing pad 26 Non-contact displacement meter 27 Carrier 28 Silicon wafer 29 Abrasive tray 30 Abrasive 31 Abrasive distribution pipe 32 Cooling temperature control device 33 Abrasive tank 34 Abrasive feed pipe 35 Abrasive return pipe 35 36 Abrasive pump

Claims (2)

  A plurality of carriers that hold the work piece are arranged at equal intervals between the sun gear and the internal gear incorporated in the horizontal plane, and after inserting the silicon wafer as the work piece, the upper polishing platen is lowered. The planetary motion that rotates and revolves the carrier while supplying the abrasive in which the colloidal silica is turbid to the PH9-12 polishing liquid while being sandwiched between the lower polishing surface plate and the relative rotational motion of the upper and lower polishing surface plates In a parallel flat polishing machine that performs simultaneous polishing, the shape displacement of the upper and lower polishing surface plate is non-contact displacement in order to compensate for the deterioration of the plane accuracy of the upper and lower polishing surface plate due to the processing heat generated by polishing the silicon wafer. The flow of cooling water, the temperature of the upper and lower polishing surface plate, and the flow rate and temperature of the abrasive are automatically controlled so that the processing surface of the upper and lower polishing surface plate that changes to concave or convex is maintained flat. Polishing method that.   2. The temperature control method for a polishing apparatus according to claim 1, wherein a decrease in planar accuracy of the processed surface of the upper and lower polishing surface plate is corrected in response to heat generated from the periphery of the polishing apparatus by processing the wafer.

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